1. Field of the Invention
This invention relates to a vaccine for swine dysentery.
2. Description of the Prior Art
It is recognised that pigs which have recovered from swine dysentery (SD) eventually become immune to subsequent challenge. However, to be solidly resistant they must have recovered without the aid of antibiotic treatment. This implies that prolonged and intensive antigenic stimulation at the surface of the large intestine is necessary to produce immunity. The poor degree of protection afforded by current vaccines suggests that such stimulation is difficult to mimic artificially.
U.S. Pat. No. 4,100,272 (R. D. Glock et al.) describes a swine dysentery vaccine of killed cells of a virulent (pathogenic) isolate of Treponema hyodysenteriae, for parenteral administration. The isolate must be virulent: attenuated or nonvirulent isolates are said not to be desirable. Two isolates are disclosed by deposition in the ATCC under Nos. 31212 and 31287.
U.S. Pat. No. 4,152,413 (R. A. Goodnow) describes a swine dysentery vaccine of killed cells of a virulent isolate of Treponema hyodysenteriae, for oral administration. The isolates must be virulent: attenuated or non-virulent isolates are said not to be desirable. The same two isolates as above are disclosed for the oral vaccine. The specification recommends dosing the pigs with the oral vaccine every day for 5 days, or a "combination procedure" believed to enhance the effectiveness of the oral administration. The procedure involves a previous administration of the same vaccine parenterally, e.g. subcutaneously or intraperitoneally. Such a procedure is described in more detail in U.S. Pat. No. 4,152,415 (D. L. Harris et al.).
All the above U.S. Patents relate exclusively to killed vaccines and emphasise the requirement that the strain be virulent. Other virulent (pathogenic) strains have been used experimentally in killed vaccines.
An avirulent variant of Treponema hyodysenteriae has been isolated from herds with no history of SD. This isolate administered orally to susceptible pigs did not produce clinical symptoms of disease or afford protection against subsequent challenge with a virulent (pathogenic) strain (P18A) of T. hyodysenteriae. See R. J. Lysons (the present inventor) et al., Proceedings of the International Pig Veterinary Society Congress, 1982, page 40. None of these isolates was made publicly available.